Storable propellant compositions



3,l58,% Patented Dec. 1, 1964 3,158 995 STORABLE PROPELLANT CSMPGSITEONfi Robert W. Sprague, Santa Ana, and Renee G Evans, Pasadena, Caiif., assignors to North American Aviation, Inc.

7 No Drawing. Filed Feb. 28, 1962, Ser. No. 176,886

6 Claims. (Cl. 60-354) This invention relates to improved rocket propellant fuels. More particularly, this invention relates to improved hydrazine-based rocket fuels and a method of operating the rocket engine utilizing these fuels.

Hydrazine is a well known rocket motor fuel having :1

relatively high specific impulse I defined as thrust in pounds divided by the total mass flow of fuel and oxidizer in pounds per second. Hydrazine, however, has a high freezing point of substantially 34 F. This makes hydrazine unattractive as a fuel for rocket propulsion systems operating in areas where the temperature falls below this figure. Research activity in the field of propellant compositions has been directed toward obtaining improved fuel composition which would have the high specific impulse of hydrazine but which would have a much lower solidification or freezing point. Therefore, a need exists for a fuel having a low freezing point and a high specific impulse when used with a storable oxidizer.

Previously, in order to obtain a fuel with a wide liquid range, a sacrifice has been made in the density impulse of the fuel I which is defined by the formula:

MR (mixture ratio) =ratio of the oxidizer consumption The density impulse of afuel is an important factor in the design of a missile system because it indicates the impulse obtainable from a given volume of fuel. Since the volume capacity of a missile is limited, it is thus obviously desirable to obtain the highest impulse from a given volume of fuel. Hydrazine has a relatively high density impulse. As a result, it is desirable to maintain or approximate this high densityirnpulse. of the hydrazine in addition to lowering its freezing point while keeping the specific impulse high.

It is an object of this invention to provide a new hydrazine-based fuel. Another object of this invention is to provide a storable rocket fuel or composition possessing a high specific impulse. It is also an object of this invention to provide a storable rocket fuel. A further object of the invention is to provide a rocket fuel composition having a low freezing point. Another object of this invention is to provide a novel rocket fuel having a high density impulse. A still further object of the invention is to provide a method for operating a rocket engine. Im-

portant other objects of thisinvention will become apparent in the discussion which follows.

It has been found that the above objects of this invention can be accomplished by the addition to a hydrazine of hydrogen chloride, HCl, and a polyhydric alcohol, in an amount suflicient to decrease the freezing point of the hydrazine fuel at least 40 F.

Hence, an embodiment of this invention comprises a method of operating a rocket engine comprising ejecting from the reaction chamber of the engine a gaseous product produced by a combustion of an oxidizer and hydrazine-based fuel having therein hydrogen chloride and a polyhydric alcohol fuel and oxidizer being injected in separate streams into the combustion or reaction chamber.

The polyhydric alcohol used in this invention has the general formula: OH OH a. U. l L' J wherein xis an integer from 0 to 4. Examples of such alcohols include ethylene glycol, glycerol, tetritol, pentitol and hexitol. Particularly preferred because of its low molecular weight and low viscosity is ethylene glycol.

It has been found that compositions comprising from 55 to 92 weight percent of hydrazine, from 3 to 18 weight percent ofHCl and from 3 to 30 weight percent of a polyhydric alcohol give greatly improved density and OH (EH.

freezing point results. The relative proportions of the two additives,HCl and the polyhydric alcohol, can cause the density and freezing point properties of the hydrazine composition to vary substantially. The proportions of each additive can thus be chosen to optimize particular properties according to the actual needs of the given application. For example, higher proportions of HCl will increase the density of the mixtures but also will tend to produce a higher viscosity. It is preferred that from 3 to 18 percent by weight of hydrogen chloride, HCl, and from 3 to 30 percent by weight of the polyhydric alcohol be added to hydrazine. Particularly good results are obtainable when from 5 to 15 percent by weight HCl and from 5 to 20 weight percent of the polyhydric alcohol is added to the hydrazine. An outstanding composition having an extremely low freezing point and a high specific impulse and density impulse is comprised of 75.5 weight percent hydrazine, 14.5 weight percent HCl and 10 weight percent of the polyhydric alcohol.

The invention is illustrated by the following examples.

EXAMPLE I Various hydrazine fuel compositions were prepared in order to determine the effect of the additives of this invention. Hydrogen chloride and ethylene glycol were mixed into hydrazine so that a total of a IO-gram composition would be obtained. It makes no difference with re gard to the order in which the two additives. are mixed with the hydrazine. The hydrogen chloride may be first added, or conversely, the ethylene glycol may be initially added to the hydrazine. In addition to determining the freezing point of the various compositions prepared, the theoretical specific impulse (I and theoretical density (I were determined for the compositions. The parameters used in theoretically determining a specific impulse was 1000 p.s.i.a. chamber pressure expanded to 14.7

p.s.i.a., shifting equilibrium and chlorine trifiuoride as,

the oxidizer. The following table presents the results obtained from three compositions prepared in accord with this invention utilizing the aforementioned additives.

The resulting mixtures clearly show a great improve ment in the extension of the liquid range of a hydrazine fuel since hydrazine has a freezing point of +34.S F. Also the densities of the mixtures are higher than the density of the hydrazine-a desirable result, since a larger ID quantity of the mixture can be used in a given volume fuel tank. This is reflected in the good density impulse obtained from the compositions of the invention.

The hydrazine-based fuel used in the composition of the invention has the general formula:

wherein R R R and R are hydrogens or hydrocarbon groups of from 1 to 12 carbon atoms. When hydrocarbon groups are substituted for the hydrogens on hydrazine, the specific impulse of the compound is decreased, speaking in terms of rocket fuel performance. Hence, the embodiment of this invention comprises a composition in which at least about 75 percent of the total number of the R R R and R groups are hydrogen atoms. A preferred embodiment comprising the composition in which at least about 90 percent of the total of R R R and R groups in said composition as a whole are hydro gen atoms, in which case a minimum decrease of specific impulse of occasioned. Another embodiment is a composition in which the hydrazine-hydrogen type compound has at least one hydrogen atom attached to each nitrogen, as when R R are hydrogen atoms. In the latter instance, performance in physical properties of the hydrazine compound as a rocket fuel are enhanced.

An especially preferred embodiment of this invention comprise a composition where the R R R and R groups are substantially all hydrogen atoms, in which case the particular hydrazine-containing composition has the maximum specific impulse in proportion to its hydrazine content. The hydrocarbon groups which replace the hydrogen atoms, on the hydrazine, have from about 1 to about 12 carbon atoms. Since, however, the specific impulse decreases the number of carbon atoms in the hydrocarbon group, it is preferable that the latter have from one to about eight carbon atoms. The hydrocarbon groups can be alkyl, cycloalkyl, aryl, arylkyl, and the like. Nonlimiting examples of hydrazine compounds are hydrazine, methylhydrazine, dimethylhydrazine, trimethylhydrazine, tetramethylhydrazine, ethylhydrazine, diethylhydrazine, methylethylhydrazine, propylhydrazine, dibutylhydrazine, phenylhydrazine, disphenylhydrazine, methylphenylhydrazine, etc. Particularly preferred is hydrazine, monornethylhydrazine, a mixture of 90 weight percent hydrazine and weight percent monomethylhydrazine, MMH, and unsymmetrical dimethylhydrazine, UDMH.

EXAMPLE II Various fuel compositions may be prepared in accordance with the teachings of this invention utilizing the polyhydric alcohols disclosed, and varying the percentages of the components within the aforegoing ranges. The following Table II sets forth examples of some of the various compositions.

Additional compositions can comprise 75 weight percent methylphenylhydrazine, weight percent HCl and i 10 weight percent ethylene glycol; 60 weight percent tetramethylhydrazine, 18 weight percent HCl and 22 weight percent ethylene glycol.

Various oxidizers may be used in combination with the fuels of this invention. These oxidizers include: halogens including interhalogens which may be chlorine, bromine, fluorine, chlorinetrifiuoride, bromide pentafluoride, bromine monofiuoride, chlorine monofluoride, iodine pentafiuoride, bromine chloride, and iodine chloride; oxides and hydrides of nitrogen which may be nitric oxide, nitrogen dioxide, nitrous oxide, nitrogen trioxide, nitric acid, nitrogen tetrom'de, and hydrozoic acid; compounds of a halogen and one or more elements having atomic numbers of 7 and 8 which may be nitrogen trichloride, nitrosyl chloride, chlorine azide, nitrosyl bromide, nitrogen fluoride, nitrosyl fluoride, nitryl fluoride, nitrogen trifluoride, chlorine monoxide, chlorine pentoxide, chlorine hexoxide, chlorine dioxide, oxygen difiuoride, and perchloryl fluoride; strong oxidizing inorganic peroxy acids including chlorosulphonic acid, phosphoric acid, pyrophosphoric acid, fluorosulphonic acid, sulphuric acid, nitric acid, hexafluorophosphon'c acid; carboxylicacids may be caproic acid, acetic acid, formic acid, butyric acid, lactic acid, and acrylic acid; oxygen and ozone; hydrogen hydrogen peroxide; tetranitramethane; and pentaborane.

Minor amounts of other compounds may be added to the compositions of this invention in order to improve thermal stability, for example, such additives include ethylene diamine tetraacetic acid, S-amino tetrazole hydrate, o-phenanthroline, ethylene diamine, and cyanoguanidine.

The novel fuel compositions of this invention may be utilized in conventional liquid propulsion rocket engines. Thus, an embodiment of this invention involves a method of operating a conventional liquid rocket engine utilizing as a fuel, therefore, the herein compositions. A conventional liquid engine system as described on page 9 of the book Rocket Propulsion Elements, by George P. Sutton (1949), published by John Wiley and Sons, New York, comprises storage means for the fuel and oxidizer used, an outer casing defining an engine chamber, the casing having on the downstream end thereof an exhaust nozzle and an injector means situated on the upstream end of the casing. A conventional supply means supplies the fuel and oxidizer from the storage tanks to the injector head. The method of operating such an engine would comprise storing the fuel and oxidizer in the separate means provided, feeding them to the injector head from where they are injected into the combustion chamber in separate streams to be intimately mixed and ignited because of their hypergolicity or with the aid of an electric spark and ejecting from the exhaust nozzle portion of the engine the combustion gases to create the desired useful thrust. In such a method of operation, chlorinetrifluoride may be stored as the liquid oxidizer while the fuel composition may typically be 75.5 weight percent hydrazine, 14.5 weight percent HCl and 10 weight percent C H O Although the invention has been described and illustratcd in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. A composition of matter comprising:

an organic hydrazine,

from 3 to 18 percent by weight of the total composition of hydrogen chloride and from 3 to 30 percent by weight of the total composition of a polyhydric alcohol having the general forwherein x is an integer from 0 to 4. 10 percent by weight of the composition of a polyhydric 2. The composition of claim 1 wherein said polyhydric alcohol having the general formula: alcohol is ethylene glycol.

OH I-OH-I 0H 3. A composrtlon of matter comprlslng J (l: 4 an organic hydazlne, 5 2 I J from 5 to 15 percent by weight of the total composi- H x tion of hydrogen chloride and from 5 to 20 percent by weight of the total composition of a polyhydric alcohol having the general formula:

wherein x is an integer from 0 to 4. 5. The composition of claim 3 wherein said polyhydric alcohol is ethyleneglycol. l0 6. In a conventional method of operating a liquid propellant rocket motor, the improvement comprising igniting as the fuel the composition of claim 1.

illi Z3.

References Cited in the file of this patent UNITED STATES PATENTS 2,521,026 Solomon Sept. 5, 1950 8,888 Ryker Oct. 30, 1956 Whmm x 18 i Integer fmm 0 to 2,943,927 Audrieth et a1 July 5,1960 4- A composltlon of matter comprising: 2,982,637 Kruse May 2 1961 75.5 percent by weight of the total composition of a 20 hydrazine 14.5 percent by weight of the total composition of hydrogen chloride and OTHER REFERENCES Audrieth: The Chemistry of Hydrazine, John Wiley & Sons, 1951, pp. 173-174. 

1. A COMPOSITION OF MATTER COMPRISING: AN ORGANIC HYDRAZINE, FROM 3 TO 18 PERCENT BY WEIGHT OF THE TOTAL COMPOSITION OF HYDROGEN CHLORIDE AND FROM 3 TO 30 PERCENT BY WEIGHT OF THE TOTAL COMPOSITION OF A POLYHYDRIC ALCOHOL HAVING THE GENERAL FORMULA:
 6. IN A CONVENTIONAL METHOD OF OPERATING A LIQUID PROPELLANT ROCKET MOTOR, THE IMPROVEMENT COMPRISING IGNITING AS THE FUEL THE COMPOSITION OF CLAIM
 1. 